add simulation test for sort_demo

This test doesn't use any hardware, but it runs in a HDL simulation program, e.g. ISim.

This test used to be in the mehari repository. If you want to see its development, look at commit d26444ca to 081b3353:
https://github.com/BBBSnowball/mehari/commit/d26444cace07d34eb44e6ca7ac1054f7658bf1d3
add script to run sort_demo test